October 19, 2021
Earth is the third closest planet to the Sun, the densest and the fifth largest of the eight planets in the Solar System. It is also the largest of the four telluric planets. It is sometimes referred to as the Blue World or Planet. Home to millions of species of living beings, including humans, Earth is the only celestial body where life is known to exist. The planet formed 4.56 billion years ago, and life emerged on its surface a billion years later. Since then, the Earth's biosphere has significantly altered the planet's atmosphere and other abiotic factors, allowing the proliferation of aerobic organisms, as well as the formation of an ozone layer, which, together with the Earth's magnetic field, blocks harmful solar radiation, allowing life on the planet. The planet's physical properties, as well as its geological history and orbit, allowed life to persist during this period. The Earth is believed to be able to support life for at least another 500 million years. Its outer surface is divided into several rigid segments, called tectonic plates, which migrate over the Earth's surface over millions of years. About 71% of the Earth's surface is covered by saltwater oceans, with the remainder consisting of continents and islands, which contain many lakes and other bodies of water that contribute to the hydrosphere. It is not known the existence of water in the liquid state in equilibrium, necessary for the maintenance of life as we know it, on the surface of any other planet. The geographic poles of the Earth are mostly covered by ice sheets or ice floes. The Earth's interior remains active, with a thick and relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid inner core, composed mostly of iron. The Earth interacts with other objects in space, in particular the Sun and Moon. At present, the Earth orbits the Sun once for every 366.26 rotations about its own axis, which is equivalent to 365.26 solar days or a sidereal year. The Earth's axis of rotation has an inclination of 23.4° in relation to the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period equal to a tropical year (365.24 solar days). The Moon is Earth's only known natural satellite, having started orbiting it 4.53 billion years ago. It is responsible for the tides, stabilizes the Earth's axial tilt and gradually slows down the planet's rotation. Between approximately 4.1 and 3.8 billion years ago, during intense late bombardment, asteroid impacts caused significant changes to the Earth's surface. The Earth's mineral resources together with the products of the biosphere provide resources that are used to support a global human population. These Earth inhabitants are grouped into some 200 sovereign states, which interact with each other through diplomacy, travel, trade, and military action. Human cultures have developed various beliefs about the planet, including its personification as a deity, the belief in a flat Earth, or that the Earth is the center of the universe, and a modern perspective of the world as an integrated environment that requires protection.